The present invention relates to notch antennas and, more specifically, to a notch antenna suitable for circularly polarized signals.
Antennas for line-of-sight (LOS) communications applications, typically in the UHF or L-band frequency bands, often have differing gain, polarization and field of view (FOV) requirements. Applications such as satellite communications (SATCOM) also impose stringent limitations on antenna size, volume and weight. Ideally, antennas for these types of applications should have reasonable gain at the horizon while still providing good coverage throughout the remainder of the hemisphere.
Typical antennas of the prior art suitable for use in these applications generally require large cavities having absorbers behind the radiating elements and suffer from low gain because of a 3 dB signal loss to the cavity. Applications benefiting from better antennas (i.e., higher gain, smaller, lighter, etc.) include SATCOM, GPS, Joint Tactical Information Distribution System (JTIDS), cellular phone, Tactical Air Navigation (TACAN), IFF transponder and digital Personal Communications Systems (PCS). Further complicating matters is the fact that several of these systems are frequently co-located on vehicles and particularly airplanes, which further drives the need for aperture and volumetric efficiency. Also, circular polarization is generally required for SATCOM and GPS applications, and polarization purity is critical for communication applications utilizing frequency reuse by means of polarization diversity.
It is, therefore, an object of the invention to provide an antenna which is capable of both linear and circular polarization.
It is an additional object of the invention to provide such an antenna having high polarization purity for circularly polarized signals.
It is another object of the invention to provide a modified notch antenna capable of performing these objectives.
It is still another object of the invention to provide a modified notch antenna which is nestable within itself at a smaller size for simultaneously accessing a higher frequency band using the same aperture and volume.
The present invention features both a low profile, broadband antenna as well as a notch antenna with a unique signal feed. The broadband antenna includes an active conductive edge having a shape which approximates a quadratic curve. Two identical elements may be used in an opposed manner to form signals across their respective active edges, and two pairs of opposed identical elements may be used in quadrature for handling circularly polarized signals with a high degree of polarization purity. The quadratic curvature of the elements can provide sufficient space to co-locate a second, smaller antenna within the same volume and aperture as the larger antenna.
In another form, a notch antenna includes a slot formed between the active conductive element and ground, which slot is used for coupling signals through the antenna. This arrangement can be used in quadrature to provide circularly polarized signals with high polarization purity.